This study is designed to investigate the activity of Parathyroid extract, Prostaglandin E2 and Phospholipase A2 on bone in mouse calvarium tissue culture. By light microscopic quantitative analysis and ultrastructural analysis, bone cells are examined for eveidence of morphologic changes due to these agents. The kinetics of osteoclast augmentation by mononucleated cells and alterations in the metabolism of bone cells in bone resorption in vitro, are quantitated by means of radioactive isotope localization. Parathyroid extract induces bone resorption in vitro, and Prostaglandin E2 and Phospholipase A2 enhance resorption in various bone systems. Parathyroid acts on the cellular level to inhibit the formation of new bone and to induce the formation of osteoclasts, the cell responsible for the pathologic bone loss in chronic destructive periodontal disease. Prostaglandin, a local or cellular hormone, may be an important mediator or modulator of chronic inflammation and pathologic bone resorption, and seems to act in a fashion similar to parathyroid hormone. Little is known about phospholipase, which was first shown to effect bone resorption in the calvarium system. This research is designed to present new evidence about the net bone loss seen in periodontal pathology.